Thermo Pride Gas/Propane Furnace Induced Draft Highboy/Counterflow/Horizontal MHA1 - Manual (Page 20)

All installations and services must be performed by qualified service personnel.
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Figure 4: Vent Connection to Inducer
A self-tapping sheet metal screw and high temperature sealant such as Dow
Corning 736 or General Electric RTV106 (temperature rating 480
°F minimum)
should be used to secure both the flue pipe (MHA1/MDA1-50), and the Thermo
Products supplied 4 in. adapter (MHA1/MDA1-75, MHA1/MDA1-100,
MHA1/MDA1-125) to the outlet of the inducer. If using other than a self-tapping
sheet metal screw to secure the flue pipe to the inducer, a starter hole must be
drilled in the inducer before inserting the screw (refer to Figure 4) to avoid
damage to the inducer housing.